1. Field of Inventions
The present inventions relate generally to devices for performing therapeutic operations on body tissue.
2. Description of the Related Art
There are many instances where electrosurgical devices are used to form therapeutic lesions in tissue. Therapeutic lesions are frequently formed to treat conditions in the heart, prostate, liver, brain, gall bladder, uterus, breasts, lungs and other solid organs. Electromagnetic radio frequency (“RF”) may, for example, be used to heat and eventually kill (i.e. “ablate”) tissue to form a lesion. During the ablation of soft tissue (i.e. tissue other than blood, bone and connective tissue), tissue coagulation occurs and it is the coagulation that kills the tissue. Thus, references to the ablation of soft tissue are necessarily references to soft tissue coagulation. “Tissue coagulation” is the process of cross-linking proteins in tissue to cause the tissue to jell. In soft tissue, it is the fluid within the tissue cell membranes that jells to kill the cells, thereby killing the tissue. The tissue coagulation energy is typically supplied and controlled by an electrosurgical unit (“ESU”) during the therapeutic procedure. More specifically, after an electrosurgical device has been connected to the ESU, and the electrodes or other energy transmission elements on the device have been positioned adjacent to the target tissue, energy from the ESU is transmitted through the energy transmission elements to the tissue to from a lesion. The amount of power required to coagulate tissue ranges from 5 to 150 W.
Clamps that carry electrodes or other energy transmission elements on opposable clamp members are used in a wide variety of electrophysiology procedures, especially those in which the physician intends to position electrodes on opposite sides of a body structure. Examples of clamp based devices which carry energy transmission elements are disclosed in U.S. Pat. No. 6,142,994, and U.S. Patent Pub. No. 2003/0158547 A1, which are incorporated herein by reference. In a typical clamp based procedure, a clamp will be used by the physician to position energy transmission surfaces (such as the outer surface of the exposed portion of the energy transmission elements) on opposite sides of a tissue structure. Energy may then be transmitted through the tissue from one energy transmission surface to the other, which is commonly referred to as bipolar energy transmission, or from each of the energy transmission surfaces to an indifferent electrode positioned at a remote location such as the patient's skin, which is commonly referred to as unipolar energy transmission.
Surgical probes are another example of devices that may be used in electrophysiology procedures. Surgical probes used to create lesions often include a handle, a relatively short shaft that is from 4 inches to 18 inches in length and either rigid or relatively stiff, and a distal section that is from 1 inch to 10 inches in length and either malleable or somewhat flexible. One or more coagulation electrodes or other energy transmission devices are carried by the distal section. Surgical probes are used in epicardial and endocardial procedures, including open heart procedures and minimally invasive procedures where access to the heart is obtained via a thoracotomy, thoracostomy or median sternotomy. Exemplary surgical probes are disclosed in U.S. Pat. No. 6,142,994.
Tissue contact is an important issue in any electrophysiology procedure. With respect to clamp based procedures, for example, the failure to achieve and maintain intimate contact between the tissue and energy transmission surfaces can result in gaps in what were intended to be continuous linear or curvilinear lesions. With respect to the formation of therapeutic lesions in the heart to treat cardiac conditions such as atrial fibrillation, atrial flutter and arrhythmia, such gaps may result in a failure to cure the arrhythmia and atrial flutter or may create atrial flutter. Moreover, atrial flutter created by gaps in linear lesions can difficult to cure. Poor contact between the tissue and energy transmission surfaces can also result in lesions that are not transmural. Lesions which are not transmural may, in turn, fail to cure the patient's arrhythmia or other medical condition.
One method of insuring the proper level of contact in clamp based electrophysiology procedures is to configure the clamp in such a manner that there is a predetermined (i.e. preset) spacing between the energy transmission surfaces when the clamp is in the closed orientation that corresponds to the thickness of the target tissue structure. In addition to insuring intimate tissue contact, the preset spacing also prevents the mechanical damage to tissue (e.g. cutting through the tissue structure) that can occur when the spacing between the energy transmission surfaces is less than the thickness of the target tissue structure when the clamp is closed. For example, electrophysiology clamps that are intended to position energy transmission surfaces on opposite sides of the tissue around the pulmonary veins have a closed orientation spacing of about 2 mm between the energy transmission surfaces.
The present inventors have determined that conventional clamp based electrophysiology devices are susceptible to improvement. More specifically, the present inventors have determined that there are procedures where a physician may wish to form lesions in tissue structures with different thicknesses. The use of a conventional clamp based electrophysiology device with a preset spacing between the energy transmission surfaces can hamper such procedures because a preset spacing that is large enough to accommodate the larger tissue structures may be too large to facilitate intimate tissue contact with the smaller tissue structures. As such, the use of a single conventional clamp based electrophysiology device in procedures that involve tissue structures of varying thickness may result in mechanical damage to tissue and/or lesions that are not continuous or transmural.
Another important issue in electrophysiology procedures is energy transmission and, more specifically, the electrical resistivity on the structure that is in contact with tissue. In some clamp and surgical probe based electrophysiology devices that include electrodes, the exposed portions of the electrodes are covered with porous, wettable structures that are configured to be saturated with and retain ionic fluid (such as saline) prior to use. Tissue coagulation energy may be transmitted to (or to and from) the electrodes by way of the ionic fluid. The present inventors have determined that conventional porous, wettable structures are susceptible to improvement and, in particular, that the electrical resistance across the porous, wettable structures should be reduced.
Still another important issue in electrophysiology procedures is confirming whether a therapeutic lesion has been properly formed during surgical procedures. Some clamp and surgical probe based electrophysiology devices employ stimulation electrodes that may be placed on tissue on one side of a lesion, or stimulation and sensing electrodes that may be placed on tissue on opposite sides of a lesion, and used to confirm whether a therapeutic lesion has been formed during surgical procedures. The present inventors have determined that such clamp and surgical probe based electrophysiology devices are susceptible to improvement.